Washington (CNN) -- The U.S. Marshals Service is confirming that it has stored more than 35,000 "whole body" images of people who had entered a U.S. courthouse in Orlando, Florida.

The images captured by millimeter wave technology are more ghost-like and far less detailed than those produced by "backscatter" machines commonly used by the Transportation Security Administration at airports nationwide.

But the Electronic Privacy Information Center, a privacy rights group that obtained the Marshals Service photos, said the disclosure shows that body imaging machines can store intrusive images of people's bodies and that the federal government will store images in the absence of strong judicial or legislative restraints.

The center and other privacy groups filed suit against the TSA this year, asking the court to bar it from using body imagers at airports.

The disclosure about the U.S. Marshals Service storing images came this week in response to a Freedom of Information Act request from the Electronic Privacy Information Center.

In a letter to the center, Justice Department attorneys agreed to give 100 images of the approximately 35,314 images that were stored on the Orlando courthouse machine from February 2 until July 28. It called the 100 images a "representative sample" of stored images.

A U.S. Marshals Office spokeswoman said the Brijot Gen2 machine in Orlando automatically stores the images to a hard drive, and security officers can look at an image of the person who just entered the machine and the two previous images. But all other images can only be accessed via an administrative passcode, spokeswoman Carolyn Gwathmey said.

Gwathmey said the stored images had never been accessed before the receipt of the Freedom of Information Act request.

Marc Rotenberg of the Electronic Privacy Information Center conceded that the Marshals Service's images are "not particularly revealing" but said this experience highlights the necessity for prohibitions on government's use of backscatter technology, which can capture far more revealing images by using X-rays to provide detailed images in or under a person's clothing.

"The only thing that is preventing the TSA from [storing images] is that we keep raising this with them," Rotenberg said.

In written comments this year to CNN, the TSA said images at airports "cannot be stored, transmitted or printed" when in normal operations.

"TSA has clearly demonstrated the extensive steps and strict measures that have been taken to protect passenger privacy," the agency said.

The images released to the Electronic Privacy Information Center were captured by a machine at the Middle District of Florida in the Orlando courthouse. The Marshals Service also tested a machine at a U.S. courthouse in Washington for about 90 days in the 2007 and 2008 time frame, Gwathmey said. During the test, the machine was not used to screen individuals entering the courthouse, she said.

That machine was returned to the vendor, and any images that may have been stored on it are no longer under agency control, the Justice Department said.